2 Shortwave uses a combination of AM, VSB, USB and LSB, with some NBFM and CW/morse code (in the case of time signal stations) as well as numerous frequencies, depending on the time of day/night, season, and solar activity level. A reasonably full list from 16 kHz to 27MHz can be found at [1]

3 Regions 1 and 3 also use Region 2's frequencies as well, with 50 to 100 kHz spacing.

1.
Radio broadcasting
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Radio broadcasting is a unidirectional wireless transmission over radio waves intended to reach a wide audience. Stations can be linked in radio networks to broadcast a radio format. Audio broadcasting also can be done via radio, local wire television networks, satellite radio. The signal types can be either analog audio or digital audio, the earliest radio stations were simply radiotelegraphy systems and did not carry audio. For audio broadcasts to be possible, electronic detection and amplification devices had to be incorporated, the thermionic valve was invented in 1904 by the English physicist John Ambrose Fleming. He developed a device he called an oscillation valve, the heated filament, or cathode, was capable of thermionic emission of electrons that would flow to the plate when it was at a higher voltage. Electrons, however, could not pass in the direction because the plate was not heated. Later known as the Fleming valve, it could be used as a rectifier of alternating current and this greatly improved the crystal set which rectified the radio signal using an early solid-state diode based on a crystal and a so-called cats whisker. However, what was required was an amplifier. The triode was patented on March 4,1906, by the Austrian Robert von Lieben independent from that, on October 25,1906 and it wasnt put to practical use until 1912 when its amplifying ability became recognized by researchers. By about 1920, valve technology had matured to the point where radio broadcasting was quickly becoming viable, however, an early audio transmission that could be termed a broadcast may have occurred on Christmas Eve in 1906 by Reginald Fessenden, although this is disputed. Charles Herrold started broadcasting in California in 1909 and was carrying audio by the next year, in The Hague, the Netherlands, PCGG started broadcasting on November 6,1919, making it, arguably the first commercial broadcasting station. In 1916, Frank Conrad, an engineer employed at the Westinghouse Electric Corporation, began broadcasting from his Wilkinsburg. Later, the station was moved to the top of the Westinghouse factory building in East Pittsburgh, Westinghouse relaunched the station as KDKA on November 2,1920, as the first commercially licensed radio station in America. The commercial broadcasting designation came from the type of broadcast license, the first licensed broadcast in the United States came from KDKA itself, the results of the Harding/Cox Presidential Election. In 1920, wireless broadcasts for entertainment began in the UK from the Marconi Research Centre 2MT at Writtle near Chelmsford, England. A famous broadcast from Marconis New Street Works factory in Chelmsford was made by the famous soprano Dame Nellie Melba on 15 June 1920 and she was the first artist of international renown to participate in direct radio broadcasts. The 2MT station began to broadcast regular entertainment in 1922, the BBC was amalgamated in 1922 and received a Royal Charter in 1926, making it the first national broadcaster in the world, followed by Czech Radio and other European broadcasters in 1923

2.
AM broadcasting
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AM broadcasting is the process of radio broadcasting using amplitude modulation. AM was the first method of impressing sound on a signal and is still widely used today. Commercial and public AM broadcasting is authorized in the wave band worldwide. Commercial AM broadcasting developed from amateur broadcasts around 1920, and was the commercially important form of radio broadcasting until FM broadcasting began after World War II. This period is known as the Golden Age of Radio, today, AM competes with FM, as well as with various digital radio broadcasting services distributed from terrestrial and satellite transmitters. AM broadcasting was the first broadcasting technology invented, the technology of amplitude modulation radio transmission was developed between 1900 and 1920. This was used for private communication and message traffic, such as telegrams. The entrepreneurs who developed AM radiotelephone transmission did not anticipate broadcasting voice, the term broadcasting, borrowed from agriculture, was applied to this new activity around 1920. Prior to 1920 there was no concept of broadcasting, or that radio listeners could be a market for entertainment. Although there were a number of broadcasts during this period. True radio broadcasting didnt begin until around 1920, when it sprang up spontaneously among amateur stations, AM remained the dominant method of broadcasting for the next 30 years, a period called the Golden Age of Radio, until FM broadcasting started to become widespread in the 1950s. AM remains a popular, profitable entertainment medium today and the dominant form of broadcasting in some such as Australia. The first AM voice transmission was made by Canadian researcher Reginald Fessenden on 23 December 1900, Fessenden is a significant figure in the development of AM radio. He helped develop one of the first – the Alexanderson alternator, the first practical continuous wave AM transmitters were based on versions of the Poulsen arc transmitter invented in 1903, and the huge, expensive Alexanderson alternator, developed 1906–1910. The modifications necessary to transmit AM were clumsy and resulted in low audio quality. Modulation was usually accomplished by a carbon microphone inserted directly in the antenna wire, the limited power handling ability of the microphone severely limited the power of the first radiotelephones, in powerful transmitters water-cooled microphones had to be used. At the receiving end, the crystal radio receivers then in use could not drive loudspeakers, only earphones. The discovery in 1912 of the ability of the Audion vacuum tube, invented in 1906 by Lee De Forest

3.
WHAS (AM)
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WHAS, known by the on air branding as News Radio 840 WHAS, is an AM radio station broadcasting in Louisville, Kentucky. It is a 50,000 Watt clear channel radio station assigned to frequency 840 kHz, with clear channel status, its nighttime signal can be heard in most of the continental U. S. and much of Canada, and even in other countries at times. The stations studios are located in the Louisville enclave of Watterson Park, WHAS is owned by iHeartMedia, Inc. Its first broadcast was on July 18,1922 and it was originally assigned the frequency of 350 kHz. On May 16,1925, the first live broadcast of the Kentucky Derby was originated by WHAS and was carried by WGN in Chicago. The call of the Derby featured an announcer who watched from the windows of one of the twin spires of Churchill Downs. On May 15,1932, WHAS changed from being an NBC affiliate, at that time, WHAS operated on 820 kHz with 10 KW power, but the output was soon increased to 25 KW as authorized by the Federal Radio Commission. During the 1937 Flood the station aired 115,000 messages, on March 30,1970 WHAS began 24-hour operation. The station was part of the local media empire ruled by the Bingham family. WHAS and its FM sister station, WAMZ were acquired by Clear Channel Communications in 1986 as part of the breakup of the Bingham familys media properties, prior to 1995, WHAS broadcast in C-QUAM AM stereo. For a time in the 1980s, it was also the Louisville affiliate for Casey Kasems American Top 40. Today the station features The Rush Limbaugh Show, The Mark Levin Show, some other personalities on the weekday lineup have included Terry Meiners on The Terry Meiners Show and Lachlan McLean on SportsTalk 840. The late morning slot has seen two changes in recent years, Francene Cucinello hosted The Francene Show until her death on January 15,2010, she was replaced that summer by Mandy Connell. In turn, Connell left in August 2013 to become the morning host on fellow iHeartMedia station KHOW in Denver, her last show on WHAS was on August 9, for several months after her move, Connell provided daily one-minute commentaries, known as Mandy Minutes, to WHAS. Connells slot was filled by Leland Conway, previously a radio host in Lexington, Kentucky and most recently Richmond, Virginia. Significant changes came to the afternoon and evening lineup in the first half of 2015, in February, McLean announced he would leave WHAS on May 15 and move to Charlotte, North Carolina, where his wife took a corporate position with the Cedar Fair amusement park company. In April, it was confirmed that Sports Talk 840 would end when McLean left WHAS, effective May 18, Meiners show was cut back by an hour, ending at 6,00 instead of 7,00. The 6–8 time slot was filled by Connell, who returned to the Louisville market with a locally focused talk show until February 2016, then long time fill in host Mary Walter took over as the permanent host and continued the local focused format

4.
CKBX
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CKBX is a Canadian radio station, which broadcasts at 840 AM in 100 Mile House, British Columbia. Owned by Vista Broadcast Group, the airs a country music format and is branded as Country 840 AM. The stations license was issued on December 15,1970 to Cariboo Broadcasters Ltd. which owned other stations. The license permitted Cariboo to operate a new AM radio station at 100 Mile House and it was allotted a frequency of 1240 kHz with a transmission power of 250 watts. Cariboo Broadcasters launched the station in 1971, in 1975, approval was granted for the station to increase its daytime transmission power from 250 to 1,000 watts. On October 9,1985, the CRTC permitted Cariboo to change CKBXs frequency from 1240 kHz to 840 kHz, on October 4,2004 at 8, 00am, CKBX changed is slogan from Wild Country to The Wolf – playing modern country and southern rock music. In 2005, Cariboo Broadcasters was acquired by the Vista Broadcast Group, in 2008, CKBX was converted to a stand-alone radio station serving 100 Mile House and area, becoming Country 840. CKCQ-FM Country 840 AM My Cariboo Now CKBX History - Canadian Communications Foundation Query the RECs Canadian station database for CKBX

5.
CFCW (AM)
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For CFCWs FM sister station, see CFCW-FM. CFCW is a Canadian radio station in Camrose, Alberta broadcasting at 840 AM, the station is owned and operated by Newcap Radio. CFCW also has studios in the NewCap Broadcast Centre in West Edmonton Mall, CFCW airs a traditional country music format with a mix of classic and current country hits. CFCW is currently ranked #6 and the 3rd most listened-to AM station in the according to the Fall 2014 Numeris data report. Most of the stations listeners live in areas outside Edmonton. CFCW started on November 2,1954 on 1230 kHz, with 250 watts power, in 1958, the station increased transmitter power up to 1,000 watts. In 1961, the station changed frequencies to 790 kHz, with 10,000 watts power, in 1976, the station increased transmitter power again to 50,000 watts, serving the Edmonton area as well. On August 1,2015, CFCW moved from 790 AM to 840 AM, on July 28,2008, Newcap applied to amend the licence by changing its frequency from 790 kHz to 840 kHz. The application was approved, however, the move was essentially voided when the then at 830 kHz in Wainwright. The Wainwright station ultimately re-applied for—and got—permission to move to FM, as a result, in spring 2015, CFCW began advertising a pending move to the 840 frequency. On August 1,2015, CFCW officially moved from 790 AM to 840 AM with nighttime power reduced to 40,000 watts to protect the cross-continent clear-channel service of WHAS, in Louisville, KY. CFCW CFCW history - Canadian Communications Foundation Query the RECs Canadian station database for CFCW Radio-Locator Information on CFCW

6.
XEMY-AM
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XHEMY-FM is a radio station in Ciudad Mante, Tamaulipas. It broadcasts on 98.7 FM and airs a format known as La Jefa. XEMY-AM840 received its concession on March 14,1966 and it was a 500-watt daytimer, later increased to 1,000 watts in the 1990s. It moved to FM in December 2011, official website radiostationworld. com, List of Tamaulipas radio stations

7.
KJFA (AM)
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KARS is a radio station licensed to Belen, New Mexico, United States, which also serves the Albuquerque area. The station is owned by American General Media, KARS also broadcasts on FM translator K275AO at 102.9 MHz at 99 watts from atop Sandia Crest. KARS airs a rock format branded as Area 102-9. The station does not feature any on-air personalities and its studios are located in Northeast Albuquerque and the transmitter tower for KARS is located in South Valley, New Mexico. KARS used to broadcast at 860 kHz at 1,300 watts during the day and 185 watts at night, however the station mostly served the Valencia County area and did not really target Albuquerque. KARS has featured a variety of programming over the years from Classic Country and Spanish-language programming as well as community information for Belen, in 2010 it began airing an Adult Standards format and later featured some religious programs before changing to the all news format in April 2012. The station used to brand itself as The Heart of New Mexico, from April 2012 until March 2013 KARS broadcast an all news format with most of its content coming from Talk Radio Networks Americas Radio News. Local news, weather and traffic reports were featured in the mornings and afternoons. KARS had filed an application with the U. S. Federal Communications Commission to move to 840 kHz at a new site, increase day power to 1,800 watts. A construction permit to make these changes was granted by the FCC on January 17,2013 and this upgrade also allows for it to re-broadcast on FM translator K275AO on 102.9 at 990 watts from atop Sandia Crest. On March 28,2013 KARS went off the air while the station upgraded its signal and it returned to the air on July 11,2013 at 840 kHz covering the Albuquerque area well during the day and improving night time coverage. The FM translator at 102.9 was also upgraded from 10 watts to 99 watts,102.9 had previously re-broadcast the classical music format from KHFM at 95.5 since signing on in late 2005. The translator was intended to improve coverage in the northeast heights, KARS launched a modern rock format branded as Area 102-9 at noon on July 24,2013. Area 102.9 launched with 10,000 songs in a row however it was four months before the station started to run commercials regularly as is sometimes common with new stations. The modern rock format originally featured music from the 1980s to current hits. Currently only K229CL93.7 uses the maximum power of 250 watts between two full powered Crest stations. On August 31,2015 KARS shifted their format from rock to active rock

8.
KMPH (AM)
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KMPH is a radio station licensed to and serving the Modesto, California area. The station is owned by Immaculate Heart Radio, through licensee IHR Educational Broadcasting, KMPH signed on in July 2006 with an Adult Standards/MOR format, with some talk programming. It effectively replaced sister station KTRB, which had operated from Modesto since 1933, the station switched to an all-talk format on March 10,2008. Pappas Telecasting shut KMPH down on August 31,2010 due to lack of revenue, KMPH later returned to air with brokered programming provided by Paulino Bernal Evangelism of Texas, then temporarily switched to a Talk format in May 2013 fed via KOMY in La Selva Beach, California. On July 30,2014, Immaculate Heart Radio Catholic programming began airing on KMPH, iHRs purchase of the station was consummated on October 30,2014 at a price of $50,000. IHeart Radio website Query the FCCs AM station database for KMPH Radio-Locator Information on KMPH Query Nielsen Audios AM station database for KMPH

9.
KSWB (AM)
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KSWB is an American radio station licensed to serve Seaside, Oregon, United States. The station, which began broadcasting in 1968, is owned and operated by John Chapman while the broadcast license is held by KSWB Productions. KSWB broadcasts a classic hits music format, in addition to its usual music programming this station also airs hourly newscasts from the Associated Press. This station began broadcasting on July 12,1968, as a station with 1,000 watts of power on a frequency of 930 kHz. The Seaside Broadcasting Corporation, with Gerald B, jerry Dennon as president, held the license for the station which was assigned the KSWB call sign by the Federal Communications Commission. Dennon, founder of Jerden Records, co-owned Seaside Broadcasting and KSWB with American folk group The Brothers Four, KSWB licensee Seaside Broadcasting Corporation was acquired by new owners on June 20,1972. The station aired a music format throughout the 1970s. In March 1981, this applied to the FCC for authorization to change broadcast frequencies from 930 kHz to 840 kHz. A construction permit to make these changes was finally issued on May 29,1984, Seaside Broadcasting Corporation encountered financial difficulties and in March 1991 applied to the FCC to transfer the broadcast license for KSWB to Kenneth S. Eiler, acting as trustee. The transfer was approved by the FCC on June 3,1991, in December 1991, trustee Kenneth S. Eiler reached an agreement to sell this station to the Monte Corporation. The deal was approved by the FCC on January 15,1992, in January 1995, the Monte Corporation reached an agreement to sell this station to Kenneth B. The deal was approved by the FCC on October 5,1995, in February 1998, Ken Ulbricht reached an agreement to sell this station to Dolphin Radio, Inc. The deal was approved by the FCC on May 11,1998, in June 1999, Dolphin Radio, Inc. reached an agreement to sell this station to New Northwest Broadcasters through their New Northwest Broadcasters II, Inc. subsidiary. The deal was approved by the FCC on August 24,1999, but the transaction was not consummated, in October 1999, Dolphin Radio, Inc. reached a new agreement to sell this station, this time to Cannon Beach Radio, LLC. The deal was approved by the FCC on January 6,2000, in January 2005, Cannon Beach Radio, LLC, reached an agreement to sell this station to KSWB Licensee, LLC. The deal was approved by the FCC on March 23,2005, in November 2016 KSWB began simulcasting on FM translator K251CD98.1 FM Seaside and rebranded as Radio Clatsop

10.
KTIC (AM)
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KTIC is a radio station broadcasting a country music format. Like its sister music station KTIC-FM, it is licensed to West Point, Nebraska, the station serves eastern Nebraska and the Sioux City area. The station is owned by Nebraska Rural Radio Association and features programming from ABC Radio. The main focus of KTIC is to provide farmers with the most current market information from the Rural Radio Network. Futures Updates and Ag News plays every hour during the day at 10 and 40 minutes past each hour. News and weather updates come at the bottom of each hour with ABC news as well as more regionally centered news being the main focus, many agricultural organizations in the area have programming slots on KTIC to accommodate the interests of the farmers and ranchers in the area. KTIC is licensed to operate only during daylight hours to protect WHAS in Louisville, as such, its operating hours vary depending on the time of year. KTIC is also broadcast on translator station K252EG98.3 MHz 24 hours per day, Query the FCCs AM station database for KTIC Radio-Locator Information on KTIC Query Nielsen Audios AM station database for KTIC

11.
KXNT (AM)
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KXNT is an AM radio station licensed to North Las Vegas, Nevada, United States. KXNT is a Class B station operating on a channel frequency. WHAS in Louisville, Kentucky is the dominant Class A station on 840 AM, so KXNT must reduce its power at night, to avoid interfering with WHASs signal. KXNT operates at 50,000 watts by day and 25,000 watts at night, KXNT is licensed to broadcast in the HD radio format. It is also heard on the HD-2 channel of sister station 100.5 KXQQ-FM, KXNT has been granted an FCC construction permit to move to the KXST transmitter site and decrease night power to 10,000 watts. KNXT airs both local and nationally syndicated talk shows, weekday programs include This Morning, Americas First News with Gordon Deal, Heidi Harris, Rush Limbaugh, Dave Ramsey, Alan Stock, Chad Benson and Coast to Coast AM with George Noory. Weekends feature shows on money, health, law, real estate, home repair, syndicated hosts include Kim Komando, Bill Cunningham, Bill Handel, Ric Edelman and Robert Kiyosaki. Some hours are paid Brokered programming, KNXT carries CBS Radio News and financial reports from Bloomberg Radio. It has a local alliance with Channel 13 KTNV-TV, the ABC TV Network affiliate in Las Vegas. KXNT signed on the air in 1986 with the call letters KVEG, airing a talk, KVEG had a wide variety of talent including Sam Greenfield, Dominick Brascia, Lou Epton, Irwin Schiff and the syndicated Tom Leykis. In 1997, KVEG changed its letters to KXNT with the NT standing for News/Talk. The station moved to a more traditional Talk Radio line up, airing Rush Limbaugh, other shows included Dr. Laura and Bill Handel. Between August 16,2010 and September 4,2015, programming on KXNT had been simulcast on its sister FM station 100.5 KXNT-FM, to give listeners who prefer FM that option. That station now airs a Rhythmic Hot AC format, under the new call sign KXQQ-FM, while 840 KXNT continues with its talk format on AM

12.
WBHY (AM)
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WBHY is a radio station broadcasting a Christian radio format. Licensed to Mobile, Alabama, USA, the serves the greater Mobile area. The station is owned by Goforth Media, Inc. The station was assigned the WBHY call letters by the Federal Communications Commission on December 23,1984, WBHY official website Query the FCCs AM station database for WBHY Radio-Locator Information on WBHY Query Nielsen Audios AM station database for WBHY FCC History Cards for WBHY

13.
WCEO
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WCEO is a Spanish Contemporary radio station located in Columbia, South Carolina, USA. The station is licensed by the Federal Communications Commission to broadcast during daytime only on 840kHz with a power of 50,000 Watts. 840 AM originally signed on January 1,1994, as WCTG with a Christian/Talk format using programming from USA Radio Network, the format had failed to make a splash in the ratings and was adjusted to a secular Talk format. The station became WCEO in November 2000, but the Talk format continued, eventually, Spanish-language programming was added on weekends under time broker agreements. In late November 2004, WCEO briefly changed format to Adult Standards as Sunny 840, however, this arrangement lasted less than a month before the station changed again to Spanish Contemporary as La Tremenda, reclaiming the WCEO call letters in the process. WCEO must shut down at sundown to protect clear-channel WHAS in Louisville, the station is owned by Norsan Broadcasting WCEO, LLC. La Raza 840 Facebook Query the FCCs AM station database for WCEO Radio-Locator Information on WCEO Query Nielsen Audios AM station database for WCEO

14.
WPGS
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WPGS/840 A. M. is a radio station licensed to Mims, Florida, U. S. A. that broadcasts a rock format. The station serves all North Brevard County, Volusia County and East Orlando Florida, the station is currently owned by Wpgs, Inc. The station went on the air as WNUY on September 18, on May 1 the station changed its call sign to WPGS. In October, WPGS dropped the Talkstar radio network to become part of the smooth jazz Groove network, Query the FCCs AM station database for WPGS Radio-Locator Information on WPGS Query Nielsen Audios AM station database for WPGS

15.
Continuous wave
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A continuous wave or continuous waveform is an electromagnetic wave of constant amplitude and frequency, a sine wave. In mathematical analysis, it is considered to be of infinite duration, continuous wave is also the name given to an early method of radio transmission, in which a sinusoidal carrier wave is switched on and off. Information is carried in the duration of the on and off periods of the signal. Very early radio transmitters used a gap to produce radio-frequency oscillations in the transmitting antenna. The signals produced by these spark-gap transmitters consisted of strings of brief pulses of radio frequency oscillations which died out rapidly to zero. The disadvantage of damped waves was that their energy was spread over a wide band of frequencies. As a result they produced electromagnetic interference that spread over the transmissions of stations at other frequencies and this motivated efforts to produce radio frequency oscillations that decayed more slowly, had less damping. Manufacturers produced spark transmitters which generated long ringing waves with minimal damping and it was realized that the ideal radio wave for radiotelegraphic communication would be a sine wave with zero damping, a continuous wave. An unbroken continuous sine wave theoretically has no bandwidth, all its energy is concentrated at a single frequency, continuous waves could not be produced with an electric spark, but were achieved with the vacuum tube electronic oscillator, invented around 1913 by Edwin Armstrong and Alexander Meissner. Damped wave spark transmitters were replaced by continuous wave vacuum tube transmitters around 1920, what is transmitted in the extra bandwidth used by a transmitter that turns on/off more abruptly is known as key clicks. Certain types of power used in transmission may increase the effect of key clicks. The first transmitters capable of producing continuous wave, the Alexanderson alternator and vacuum tube oscillators, early radio transmitters could not be modulated to transmit speech, and so CW radio telegraphy was the only form of communication available. Continuous-wave radio was called radiotelegraphy because like the telegraph, it worked by means of a switch to transmit Morse code. However, instead of controlling the electricity in a cross-country wire and this mode is still in common use by amateur radio operators. In military communications and amateur radio, the terms CW and Morse code are used interchangeably. Morse code may be sent using direct current in wires, sound, or light, a carrier wave is keyed on and off to represent the dots and dashes of the code elements. The carriers amplitude and frequency remains constant during each code element, at the receiver, the received signal is mixed with a heterodyne signal from a BFO to change the radio frequency impulses to sound. Though most commercial traffic has now ceased operation using Morse it is popular with amateur radio operators

16.
Morse code
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Morse code is a method of transmitting text information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment. It is named for Samuel F. B, Morse, an inventor of the telegraph. Because many non-English natural languages use more than the 26 Roman letters, each Morse code symbol represents either a text character or a prosign and is represented by a unique sequence of dots and dashes. The duration of a dash is three times the duration of a dot, each dot or dash is followed by a short silence, equal to the dot duration. The letters of a word are separated by an equal to three dots, and the words are separated by a space equal to seven dots. The dot duration is the unit of time measurement in code transmission. To increase the speed of the communication, the code was designed so that the length of each character in Morse varies approximately inversely to its frequency of occurrence in English. Thus the most common letter in English, the letter E, has the shortest code, Morse code is used by some amateur radio operators, although knowledge of and proficiency with it is no longer required for licensing in most countries. Pilots and air controllers usually need only a cursory understanding. Aeronautical navigational aids, such as VORs and NDBs, constantly identify in Morse code, compared to voice, Morse code is less sensitive to poor signal conditions, yet still comprehensible to humans without a decoding device. Morse is, therefore, an alternative to synthesized speech for sending automated data to skilled listeners on voice channels. Many amateur radio repeaters, for example, identify with Morse, in an emergency, Morse code can be sent by improvised methods that can be easily keyed on and off, making it one of the simplest and most versatile methods of telecommunication. The most common signal is SOS or three dots, three dashes, and three dots, internationally recognized by treaty. Beginning in 1836, the American artist Samuel F. B, Morse, the American physicist Joseph Henry, and Alfred Vail developed an electrical telegraph system. This system sent pulses of current along wires which controlled an electromagnet that was located at the receiving end of the telegraph system. A code was needed to transmit natural language using only these pulses, around 1837, Morse, therefore, developed an early forerunner to the modern International Morse code. Around the same time, Carl Friedrich Gauss and Wilhelm Eduard Weber as well as Carl August von Steinheil had already used codes with varying lengths for their telegraphs. In 1837, William Cooke and Charles Wheatstone in England began using a telegraph that also used electromagnets in its receivers

17.
Very low frequency
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Very low frequency or VLF is the ITU designation for radio frequencies in the range of 3 kHz to 30 kHz and corresponding wavelengths from 100 to 10 kilometres, respectively. The band is known as the myriametre band or myriametre wave as the wavelengths range from one to ten myriametres. Due to its bandwidth, audio transmission is highly impractical in this band. The VLF band is used for a few radio navigation services, government time radio stations, since VLF waves can penetrate at least 40 meters into saltwater, they are used for military communication with submarines. The main mode of long distance propagation is an Earth-ionosphere waveguide mechanism, the Earth is surrounded by a conductive layer of electrons and ions in the upper atmosphere, the ionosphere D layer at 60 km altitude, which reflects VLF radio waves. The conductive ionosphere and the conductive Earth, form a horizontal duct a few VLF wavelengths high, the waves travel in a zigzag path around the Earth, reflected alternately by the Earth and the ionosphere, in TM mode. Therefore, VLF transmissions are very stable and reliable, and are used for distance communication. Propagation distances of 5000 to 20000 km have been realized, however, atmospheric noise is high in the band, including such phenomena as whistlers, caused by lightning. VLF waves can penetrate seawater to a depth of at least 10 to 40 meters, depending on the frequency employed, VLF waves at certain frequencies have been found to cause electron precipitation. A major practical drawback to this band is that because of the length of the waves, vertical antennas must be used because VLF waves propagate in vertical polarization, but a quarter-wave vertical antenna at 30 kHz would be 2.5 kilometers high. So practical transmitting antennas are short, a small fraction of a wavelength long. Due to their low radiation resistance they are inefficient, radiating only 10% to 50% of the power at most. With the rest of the power dissipated in the antenna/ground system resistances, Very high power transmitters are required to radiate enough power for long distance communication. Transmitting antennas for VLF frequencies are very large antennas, up to a mile across. They consist of a series of radio masts, linked at the top with a network of cables. Either the towers themselves or vertical wires serve as monopole radiators, high power stations use variations on the umbrella antenna such as the delta and trideco antennas, or multiply-tuned flattop antennas. For low power transmitters, inverted-L and T antennas are used, a large loading coil is required at the antenna feed point to cancel the capacitive reactance of the antenna to make it resonant. To minimize power dissipated in the ground, these antennas require extremely low resistance ground systems, the high capacitance and inductance and low resistance of the antenna-loading coil combination, makes it act electrically like a high Q tuned circuit

18.
Varberg Radio Station
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The Varberg Radio Station at Grimeton is a VLF transmission facility at Grimeton close to Varberg, in Halland, Sweden. It has the only working Alexanderson alternator rotating armature radio transmitter in the world and is classified as a World Heritage Site and it is an anchor site for the European Route of Industrial Heritage. The transmitter was built in 1922 to 1924, to operate at 17.2 kHz, the Grimeton VLF transmitter location is also used for shortwave transmissions, FM and TV broadcasting. For this purpose, a 260 metre high guyed steel framework mast was built in 1966 next to the containing the 40 kHz transmitter. Until the 1950s, the Grimeton VLF transmitter was used for radio telegraphy to Radio Central in Long Island, New York. From the 1960s until 1996 it transmitted orders to submarines in the Swedish Navy, in 1968 a second transmitter was installed which uses the same aerial as the machine transmitter but with transistor and tube technology. The Alexanderson transmitter became obsolete in 1996 and went out of service, however, because it was still in good condition it was declared a national monument and can be visited during the summer. On July 2,2004, the Grimeton VLF transmitter was declared a World Cultural Heritage site by UNESCO and it continues to be used on special occasions such as Alexanderson Day to transmit Morse messages on 17.2 kHz. The Grimeton/Varberg site is used by the Swedish Navy, transmitting on 40.4 kHz using call sign SRC using the vacuum tube transmitter. Therefore the special transmissions from that machine transmitter are very rare, recent transmissions from SAQ on 17.2 kHz took place on December 24,2013, June 29,2014, December 24,2014, June 28,2015 and July 3,2016. At least two regular transmissions take place each year, on the first Sunday of July and on Christmas Eve, plus one or two extra transmissions on special occasions or for testing

19.
Low frequency
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Low frequency or LF is the ITU designation for radio frequencies in the range of 30 kHz–300 kHz. As its wavelengths range from ten kilometres to one kilometre, respectively, LF radio waves exhibit low signal attenuation, making them suitable for long-distance communications. In Europe and areas of Northern Africa and Asia, part of the LF spectrum is used for AM broadcasting as the longwave band, in the western hemisphere, its main use is for aircraft beacon, navigation, information, and weather systems. A number of time signal broadcasts are also broadcast in this band, because of their long wavelength, low frequency radio waves can diffract over obstacles like mountain ranges and travel beyond the horizon, following the contour of the Earth. This mode of propagation, called ground wave, is the mode in the LF band. Ground waves must be polarized, so monopole antennas are used for transmitting. The attenuation of signal strength with distance by absorption in the ground is lower than at higher frequencies, low frequency ground waves can be received up to 2,000 kilometres from the transmitting antenna. Low frequency waves can also travel long distances by reflecting from the ionosphere, although this method. Reflection occurs at the ionospheric E layer or F layers, skywave signals can be detected at distances exceeding 300 kilometres from the transmitting antenna. In Europe and Japan, many low-cost consumer devices have since the late 1980s contained radio clocks with an LF receiver for these signals. Since these frequencies propagate by ground wave only, the precision of time signals is not affected by varying propagation paths between the transmitter, the ionosphere, and the receiver. In the United States, such devices became feasible for the market only after the output power of WWVB was increased in 1997 and 1999. Radio signals below 50 kHz are capable of penetrating ocean depths to approximately 200 metres, the longer the wavelength, the British, German, Indian, Russian, Swedish, United States and possibly other navies communicate with submarines on these frequencies. In addition, Royal Navy nuclear submarines carrying ballistic missiles are allegedly under standing orders to monitor the BBC Radio 4 transmission on 198 kHz in waters near the UK. In the US, the Ground Wave Emergency Network or GWEN operated between 150 and 175 kHz, until replaced by satellite systems in 1999. GWEN was a land based military radio communications system which could survive, the 2007 World Radiocommunication Conference made this band a worldwide amateur radio allocation. An international 2.1 kHz allocation, the 2200 meter band, is available to amateur operators in several countries in Europe, New Zealand, Canada. The world record distance for a contact is over 10,000 km from near Vladivostok to New Zealand

20.
Longwave
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In radio, longwave, also written as long wave or long-wave, and commonly abbreviated LW, refers to parts of the radio spectrum with relatively long wavelengths. The term is an one, dating from the early 20th century, when the radio spectrum was considered to consist of long, medium. Most modern radio systems and devices use wavelengths which would then have been considered ultra-short, in contemporary usage, the term longwave is not defined precisely, and its meaning varies across the world. Sometimes, part of the frequency band is included. The International Telecommunication Union Region 1 longwave broadcast band falls wholly within the low band of the radio spectrum. Broader definitions of longwave may extend below and/or above it, in the US, the Longwave Club of America is interested in frequencies below the AM broadcast band, i. e. all frequencies below 535 kHz. Because of their wavelength, radio waves in this frequency range can diffract over obstacles like mountain ranges and travel beyond the horizon. This mode of propagation, called ground wave, is the mode in the longwave band. The attenuation of signal strength with distance by absorption in the ground is lower than at higher frequencies, Low frequency ground waves can be received up to 2,000 kilometres from the transmitting antenna. Low frequency waves can also travel long distances by reflecting from the ionosphere, although this method. Reflection occurs at the ionospheric E layer or F layers, skywave signals can be detected at distances exceeding 300 kilometres from the transmitting antenna. Non-directional beacons transmit continuously for the benefit of radio direction finders in marine and they identify themselves by a callsign in Morse code. They can occupy any frequency in the range 190–1750 kHz, in North America, they occupy 190–535 kHz. In ITU Region 1 the lower limit is 280 kHz, there are government broadcast stations in the range 40–80 kHz that transmit coded time signals to radio clocks. Radio controlled clocks receive their time calibration signals with built-in long-wave receivers, long-waves travel by groundwaves that hug the surface of the earth, unlike medium-waves and short-waves. Those higher-frequency signals do not follow the surface of the Earth beyond a few kilometers and these different propagation paths can make the time lag different for every signal received. The military of the United Kingdom, Russian Federation, United States, Germany, in North America during the 1970s, the frequencies 167,179 and 191 kHz were assigned to the short-lived Public Emergency Radio of the United States. Nowadays, in the United States, Part 15 of FCC regulations allow unlicensed use of 136 kHz and this is called Low Frequency Experimental Radio

21.
Radio clock
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A radio clock or radio-controlled clock is a clock that is automatically synchronized by a time code transmitted by a radio transmitter connected to a time standard such as an atomic clock. Such a clock may be synchronized to the time sent by a transmitter, such as many national or regional time transmitters, or may use multiple transmitters. Such systems may be used to set clocks or for any purpose where accurate time is needed. The radio controlled clock will contain a time base oscillator to maintain timekeeping if the radio signal is momentarily unavailable. Other radio controlled clocks use the signals transmitted by dedicated transmitters in the shortwave bands. Systems using dedicated time signal stations can achieve accuracy of a few tens of milliseconds, GPS satellite navigation receivers also internally generate accurate time information from the satellite signals. General purpose or consumer grade GPS may have an offset of up to one second between the calculated time, which is much more accurate than 1 second, and the time displayed on the screen. Other broadcast services may include timekeeping information of varying accuracy within their signals, Radio clocks depend on coded time signals from radio stations. The stations vary in broadcast frequency, in location. In general, each station has its own format for the time code, many other countries can receive these signals, but success depends on the time of day, atmospheric conditions, and interference from intervening buildings. Reception is generally better if the clock is placed near a window facing the transmitter, there is also a transit delay of approximately 1 ms for every 300 km the receiver is from the transmitter. A number of manufacturers and retailers sell radio clocks that receive coded time signals from a radio station, one of the first radio clocks was offered by Heathkit in late 1983. Their model GC-1000 Most Accurate Clock received shortwave time signals from radio station WWV in Fort Collins and it automatically switched between WWVs 5,10, and 15 MHz frequencies to find the strongest signal as conditions changed through the day and year. It kept time during periods of poor reception with a quartz-crystal oscillator and this oscillator was disciplined, meaning that the microprocessor-based clock used the highly accurate time signal received from WWV to trim the crystal oscillator. The timekeeping between updates was thus more accurate than the crystal alone could have achieved. Time down to the tenth of a second was shown on an LED display, the GC-1000 originally sold for US$250 in kit form, US$400 preassembled, and was considered impressive at the time. Heath Company was granted a patent for its design, in the 2000s radio-based atomic clocks became common in retail stores, as of 2010 prices start at around US$15 in many countries. Clocks may have features such as indoor thermometers and weather station functionality

22.
JJY
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JJY is the call sign of a low frequency time signal radio station located in Japan. The station broadcasts from two sites, one on Mount Otakadoya, near Fukushima, and the other on Mount Hagane, the Mount Otakadoya site is located at an elevation of 790 meters. It broadcasts a 50 kW signal on 40 kHz from an umbrella top-loading antenna situated 250 meters above the ground, as of March 2011 it has been powered down and evacuated due to the Fukushima I nuclear accidents. As of April 21 it is broadcasting again but is unattended by staff and it went off air again temporarily on April 25 due to lightning, but has ever since been on air. The Mount Hagane site is located at an elevation of 900 meters and it broadcasts a 50 kW signal on 60 kHz to avoid interfering with the Otakadoya site as their signals overlap. The antenna for the Hagane site is also a top loading antenna and is situated 200 meters above the ground. This site does not have a redundant 40 kHz transmitter, so cannot act as a fallback for the Mount Otakadoya site, both carrier signals contain an identical pulse-width modulated time code and are transmitted 24 hours a day. Low frequency transmissions are used to enhance accuracy and reduce the possibility of atmospheric interference, the calculated accuracy of JJYs signal is 1×10−11. Japan Standard Time is set by an atomic clock in Tokyo. This information is sent to the stations and is used to set a caesium atomic clock at each station. These clocks are housed in a controlled and electromagnetically shielded room to prevent outside interference with the clocks. The time code format is similar to that of WWVB in the United States. Similarly to WWVB or MSF the signal of JJY is used to synchronize consumer radio-controlled clocks sold throughout Japan, each station has an identical setup of equipment. A dual set of transmitters, a primary and a backup, however, it is not possible given the current design configuration for one site to act as a lower power alternate frequency backup for the other. The backups are set to take over in the event that the primary transmission system has a failure. The Time Signal Control Room generates the standard LF signal and time code that is broadcast, the Impedance Matching Room has a matching transformer to perform impedance matching between the transmitter and the antenna. Due to the power of radio frequency signals that pass through the room. On January 30,1940, the Communications Research Laboratory, began operations of JJY as a station, broadcasting at 4,7,9

23.
Time from NPL
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The Time from NPL is a radio signal broadcast from the Anthorn Radio Station near Anthorn, Cumbria, which serves as the United Kingdoms national time reference. The time signal is derived from three atomic clocks installed at the site, and is based on time standards maintained by the UKs National Physical Laboratory in Teddington. The service is provided by Babcock International under licence from the NPL and is funded by the Department for Business, Innovation and Skills. The signal, also known as the MSF signal, is broadcast at an accurate frequency of 60 kHz and can be received throughout the UK. The signal’s carrier frequency is maintained at 60 kHz to within 2 parts in 1012, a radio station at Rugby was first operated by the Post Office from 1926, with the call-sign GBR. From 19 December 1927, it broadcast a 15.8 kHz time signal from the Royal Observatory which could be received worldwide. It consisted of 306 pulses in the five minutes up to and including 10,00 and 18,00 GMT, frequency-shift keying was added in 1967, making the signal harder to use as a frequency reference. The time signals, preceded by the callsign GBR GBR TIME in morse code, were transmitted during the 5 minutes preceding 03,00,09,00,15,00 and 21,00. Transmitter GBZ on 19.6 kHz was used as a reserve, eventually, time signals from GBR were terminated in November 1986 and it is no longer used as a frequency reference. The MSF signals started in 1950, following the pattern described below. They were originally intended to provide frequency references at 2.5,5 and 10 MHz, at first, there were announcements every fifteen minutes, beginning with the Morse code representation of MSF MSF MSF, followed by speech This is MSF, Rugby, England, transmitting. From May 1953, the signal was broadcast 24 hours a day, the 60 kHz signal finally became an uninterrupted 24-hour service in 1966, and the frequency references were discontinued in February 1988. On 27 February 2007 the NPL started tests of the new time signal transmissions from Anthorn and this station is operated by VT Communications. The formal inauguration of the facility took place on 1 April 2007, when the name of the service became The Time from NPL. The change in location and consequent change in strength can make some equipment designed to use the MSF signal fail to continue doing so. This is found more in domestic equipment not designed for optimum sensitivity, from the time signals inauguration in 1950 until 1 April 2007 it was transmitted from Rugby Radio Station near Rugby, Warwickshire. The transmitters original location meant that the clock was referred to as the Rugby clock, following its relocation in 2007 to Cumbria, the NPL now formally calls the signal The Time from NPL. The Rugby transmitters callsign was MSF, where M is one of the ITU prefixes allocated to the United Kingdom, and this resulted in the common terminology the MSF signal, which is still used by the NPL

24.
WWVB
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WWVB is a time signal radio station near Fort Collins, Colorado and is operated by the National Institute of Standards and Technology. Most radio-controlled clocks in North America use WWVBs transmissions to set the correct time. A single complete frame of time begins at the start of each minute, lasts one minute, and conveys the year, day of year, hour, minute. WWVB is co-located with WWV, an older time signal station that broadcasts on multiple short wave frequencies. While most time signals encode the time of the broadcasting nation. Radio-controlled clocks can then apply time zone and daylight saving time offsets as needed to local time. The time used in the broadcast is set by the NIST Time Scale and this time scale is the calculated average time of an ensemble of master clocks, themselves calibrated by the NIST-F1 and NIST-F2 cesium fountain atomic clocks. In 2011, NIST estimated the number of clocks and wristwatches equipped with a WWVB receiver at over 50 million. LF and VLF broadcasts have long used to distribute time. As early as 1904, the United States Naval Observatory was broadcasting time signals from the city of Boston as an aid to navigation and this experiment and others like it made it evident that LF and VLF signals could cover a large area using a relatively small amount of power. By 1923, NIST radio station WWV had begun broadcasting standard carrier signals to the public on frequencies ranging from 75 to 2,000 kHz and these signals were used to calibrate radio equipment, which became increasingly important as more and more stations became operational. Over the years, many radio navigation systems were designed using stable time, the most well-known of these navigation systems is LORAN-C, which allows ships and planes to navigate via reception of 100 kHz signals broadcast from multiple transmitters. What is now WWVB began as radio station KK2XEI in July 1956, the transmitter was located in Boulder, Colorado, and the effective radiated power was just 1.4 watts. Even so, the signal was able to be monitored at Harvard University in Massachusetts, the purpose of this experimental transmission was to show that the radio path was stable and the frequency error was small at low frequencies. In 1962, NIST began building a new facility at a site near Fort Collins and this site became the home of WWVB and WWVL, a 20 kHz transmitter that was moved from the mountains west of Boulder. The site was attractive for several reasons, one being its exceptionally high ground conductivity, which was due to the high alkalinity of the soil. It was also close to Boulder, which made it easy to staff and manage, but much farther away from the mountains. WWVB went on the air on July 5,1963, broadcasting a 5 kW ERP signal on 60 kHz

25.
DCF77
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DCF77 is a German longwave time signal and standard-frequency radio station. It started service as a station on 1 January 1959. In June 1973 date and time information was added and its primary and backup transmitter are located at 50°0′56″N 9°00′39″E in Mainflingen, about 25 km south-east of Frankfurt am Main, Germany. The transmitter generates a power of 50 kW, of which about 30 to 35 kW can be radiated via a T-antenna. DCF77 is controlled by the Physikalisch-Technische Bundesanstalt, Germanys national physics laboratory and it is operated by Media Broadcast GmbH, on behalf of the PTB. With Media Broadcast GmbH, a temporal transmission availability of at least 99. 7% per year or under 26.28 hours of annual downtime has been agreed upon, most service interruptions are short-term disconnections of under two minutes. Longer lasting transmission service interruptions are generally caused by strong winds and this manifests itself in electrical detuning of the antenna resonance circuit and hence a measurable phase modulation of the received signal. When the maladjustment is too large, the transmitter is temporarily out of service. In the year 2002 almost 99. 95% availability or just over 4.38 hours of downtime was realized, the timestamp sent is either in Coordinated Universal Time +1 or UTC+2 depending on daylight saving time. The highly accurate 77.5 kHz carrier signal is generated from local atomic clocks that are linked with the German master clocks at the PTB in Braunschweig, the DCF77 time signal is used for the dissemination of the German national legal time to the public. Radio clocks and watches have been popular in Europe since the late 1980s and, in mainland Europe. The DCF77 station signal carries an amplitude-modulated, pulse-width coded 1-bit/s data signal, the same data signal is also phase modulated onto the carrier using a 512-bit long pseudorandom sequence. The transmitted data signal is repeated every minute, since 2003,14 previously unused bits of the time code have been used for civil defence emergency signals. This is a service, aimed to one day replace the German network of civil defence sirens. Since 22 November 2006 the DCF77 transmitter uses bits 1–14 to transmit warning messages, under responsibility of the German Federal Office of Civil Protection and Disaster Assistance, warnings to the population can be transmitted using these 14 bits. As a further extension of the information content transmitted by DCF77, the forecast data is provided by and under responsibility of the Swiss company Meteo Time GmbH and is transferred in a proprietary transfer protocol. The same 14 bits are employed in a way that ensures compatibility with the protocols of the warning messages. For decoding the weather forecast data a license is required, since the bits previously reserved for the PTB are used, older radio clocks should not be affected by the weather data signal

26.
TDF time signal
–
TéléDiffusion de France broadcast the TDF time signal, controlled by LNE–SYRTE, from the Allouis longwave transmitter at 162 kHz, with a power of 2 MW. It was also known as FI or France Inter because the signal was formerly best known for broadcasting the France Inter AM signal and this signal ceased at the end of 2016, but the transmitter remains in use for its time signal and other digital signals. In 1980, the first atomic clock was installed to regulate the carrier frequency and it requires a more complex receiver than the popular DCF77 service, but the much more powerful transmitter gives it a much greater range of 3500 km. The signal is almost continuous but there is a regularly scheduled interruption for maintenance every Tuesday and this used to be from 01,03 to 05,00, but with the cessation of audio signals, it has been moved to 08,00 to 12,00. The signal was formerly 2000 kW, but has reduced to 1500 kW. TéléDiffusion de France uses an amplitude modulated longwave transmitter station, Time signals are transmitted by phase-modulating the carrier by ±1 radian in 0.1 s every second except the 59th second of each minute. This modulation pattern is repeated to indicate a binary one, the time transmitted is the local time of the upcoming minute. Bit 15 is reserved to indicate abnormal transmitter operation, as extensions to the DCF77 code, bit 14 is set during public holidays, and bit 13 is set the day before public holidays. Unlike DCF77, bit 19 is not used for leap second warnings, instead, bit 1 is used to warn of a positive leap second, and bit 2 is used to warn of a negative leap second. In case of a second, an additional zero bit is inserted between bits 2 and 3. The relative uncertainty of the frequency is 2 parts in 1012. One signal element is sent at each second between 0 and 58. Two signal elements are sent in sequence to represent a binary one, during ramp B of the initial signal element, the exact point the signal phase is at zero represents the top of the UTC second. Since the phase is the integral of the frequency, this phase modulation at 40 rad/s corresponds to a square frequency modulation with a deviation of 20/π ≈6.37 Hz. Both the average phase and the frequency deviation are thus zero. Additional non-timing data is sent by phase modulation during the rest of each second, but the second marker is always preceded by 100 ms without any phase modulation. The signal is not phase-modulated at all during the 59th second past the minute, loop antenna Allouis longwave transmitter, the facility used for its transmission. Standard Frequency and Time Signal Stations On Longwave and Shortwave, archived from the original on 2006-08-18

27.
ITU Region
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The International Telecommunication Union, in its International Radio Regulations, divides the world into three ITU regions for the purposes of managing the global radio spectrum. Each region has its own set of frequency allocations, the reason for defining the regions. Region 1 comprises Europe, Africa, the former Soviet Union, Mongolia, the western boundary is defined by Line B. Region 2 covers the Americas including Greenland, and some of the eastern Pacific Islands, the eastern boundary is defined by Line B. Region 3 contains most of non-FSU Asia east of and including Iran, the definition of the European Broadcasting Area uses some of the definitions of Region 1

Morse code is a method of transmitting text information as a series of on-off tones, lights, or clicks that can be …

Typical "straight key". This U.S. model J-38, was manufactured in huge quantities during World War II. The signal is "on" when the knob is pressed, and "off" when it is released. Length and timing of the dots and dashes are entirely controlled by the telegraphist.

Morse code receiver, recording on paper tape

A U.S. Navy Morse Code training class in 2015. The sailors will use their new skills to collect signals intelligence.

A commercially manufactured iambic paddle used in conjunction with an electronic keyer to generate high-speed Morse code, the timing of which is controlled by the electronic keyer. Manipulation of dual-lever paddles is similar to the Vibroplex, but pressing the right paddle generates a series of dahs, and squeezing the paddles produces dit-dah-dit-dah sequence. The actions are reversed for left-handed operators.

AM broadcasting is a radio broadcasting technology, which employs amplitude modulation (AM) transmissions. It was the …

One of the earliest radio broadcasts, French soprano Mariette Mazarin singing into Lee de Forest's arc transmitter in New York City on February 24, 1910.

Lee de Forest used an early vacuum-tube transmitter to broadcast returns for the Hughes-Wilson presidential election returns on November 7, 1916, over 2XG in New York City. Pictured is engineer Charles Logwood

Nellie Melba making a broadcast over the Marconi Chelmsford Works radio station in England on 15 June 1920

Farmer listening to U.S. government weather and crop reports using a crystal radio. Public service government time, weather, and farm broadcasts were the first radio "broadcasts".

"Trideco" antenna tower array at the US Navy's Naval Radio Station Cutler in Cutler, Maine, USA. The central mast is the radiating element, while the star-shaped horizontal wire array is the capacitive top load. About 1.2 miles in diameter, it communicates with submerged submarines at 24 kHz at a power of 1.8 megawatts, the most powerful radio station in the world.

Another type of large VLF antenna: the "valley-span" antenna, consisting of multiple horizontal topload cables spanning a valley, fed in the center by vertical radiators. This example is at the US Navy Jim Creek station near Seattle, which transmits on 24.8 kHz at a power of 1.2 MW.

Low frequency (low freq) or LF is the ITU designation for radio frequencies (RF) in the range of 30 kilohertz (kHz)–300 …

Atmospheric radio noise increases with decreasing frequency. At the LF band and below, it is far above the thermal noise floor in receiver circuits. Therefore, inefficient antennas much smaller than the wavelength are adequate for reception